get_adjacencies: get_adjacencies
In landscapemetrics: Landscape Metrics for Categorical Map Patterns

Description Usage Arguments Details Value Examples

Fast calculation of adjacencies between classes in a raster

1	get_adjacencies(landscape, neighbourhood = 4, what = "full", upper = FALSE)

`landscape`	Raster* Layer, Stack, Brick, SpatRaster (terra), stars, or a list of rasterLayers.
`neighbourhood`	The number of directions in which cell adjacencies are considered as neighbours: 4 (rook's case), 8 (queen's case) or a binary matrix where the ones define the neighbourhood. The default is 4.
`what`	Which adjacencies to calculate: "full" for a full adjacency matrix, "like" for the diagonal, "unlike" for the off diagonal part of the matrix and "triangle" for a triangular matrix counting adjacencies only once.
`upper`	Logical value indicating whether the upper triangle of the adjacency matrix should be returned (default FALSE).

A fast implementation with Rcpp to calculate the adjacency matrix for raster. The adjacency matrix is most often used in landscape metrics to describe the configuration of landscapes, is it is a cellwise count of edges between classes.

The "full" adjacency matrix is double-count method, as it contains the pairwise counts of cells between all classes. The diagonal of this matrix contains the like adjacencies, a count for how many edges a shared in each class with the same class.

The "unlike" adjacencies are counting the cellwise edges between different classes.

matrix with adjacencies between classes in a raster and between cells from the same class.

# calculate full adjacency matrix
get_adjacencies(landscape, 4)

# count diagonal neighbour adjacencies
diagonal_matrix <- matrix(c(1,  NA,  1,
                            NA,  0, NA,
                            1,  NA,  1), 3, 3, byrow = TRUE)
get_adjacencies(landscape, diagonal_matrix)

# equivalent with the raster package:
adjacencies <- raster::adjacent(landscape, 1:raster::ncell(landscape), 4, pairs=TRUE)
table(landscape[adjacencies[,1]], landscape[adjacencies[,2]])